Zaichenko A. Improving processes of electric discharge processing of blend and spark plasma sintering for obtainment of high wear-resistant carbide steels.

The thesis deals with scientific and technical problem – obtainment of metal-matrix composite materials of Fe-Ti-C-(B) system with high wear resistance, by improving an electric discharge processing of Fe, Ti and B4C powders mixture through the use of high voltage electric discharge (HED) in hydrocarbon liquid, followed by a spark-plasma sintering (SPS) of derived blend. Necessary conditions for powders dispersion and synthesis of hard phases during HED processing are theoretically found in present work. Regularities of powder mixtures HED treatment parameters connection to change of their dispersity and phase composition are experimentally determined. Mechanism of high voltage electric discharge synthesis of carbide phases during powders HED processing in hydrocarbon liquid, which includes destruction of hydrocarbon chains with synthesis of active nanocarbon of different allotropic modifications, atoms of which in conditions of significant temperatures and pressures are able to implant into metal crystal lattice, creating carbide compounds, is proposed. Dependence of synthesized carbon quantity on integral processing energy is found, which allowed ensuring stoichiometric carbide compounds synthesis conditions. Basing on the specific electric resistivity of blend the distribution of the temperature field in the cylindrical wall of the graphite matrix and parameters of spark-plasma sintering are determined, which allowed obtainment of composite metal-matrix material of Fe-Ti-C-(B) system with high density (porosity up to 1 %). Technological scheme for obtainment of materials with high wear resistance, hardness and strength is developed basing on theoretical and experimental results of thesis. Carbide steels of Fe–Ti–C system have hardness up to 56 HRC, bending strength up to 1050 MPa, abrasive wear resistance of friction for 18-20% higher than of the high speed steel P6M5. Carbide steels of Fe–Ti–B–C system have hardness up to 68 HRC, bending strength up to 1350 MPa, abrasive wear resistance of friction for 15-25% higher than of the high speed steel P6M5. Proposed composite materials and technological schemes passed industrial testing on “Zavod Kristal” Ltd. Punches for sheet metal (Fe-Ti-B-C system material) and roller carriages for thermal cutting machines (Fe-Ti-C system material) were made. In the first case the working edge resistance increased by 35% and in the second details resource increased twice.